Method of manufacturing the thermal fluid flow sensor

ABSTRACT

In a thermal sensor with a detection part and a circuit part formed on the same substrate, an insulating film for protection of the circuit part causes problems of lowering in sensitivity of a heater, deterioration in accuracy due to variation of a residual stress in the detection part, etc. A layered film including insulating films is formed on a heating resistor, an intermediate layer is formed thereon, and a layered film including insulating films is formed further thereon. The intermediate layer is specified to be a layer made up of any one of aluminum nitride, aluminum oxide, silicon carbide, titanium nitride, tungsten nitride, and titanium tungsten. This configuration enables the layered film on the upper part of the detection part to be removed using the intermediate layer as an etch stop layer, which solves problems of lowering in sensitivity, a variation in residual stress, etc. resulting from these.

CROSS REFERENCE TO RELATED DOCUMENTS

This application is a Division of U.S. application Ser. No. 13/351,157,filed on Jan. 16, 2012, now U.S. Pat. No. 8,714,008, which claimspriority to Japanese Application Nos. 2011-066964, filed on Mar. 25,2011.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2011-066964 filed on Mar. 25, 2011, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a thermal sensor and a method ofmanufacturing the thermal sensor, and more specifically, to a thermalsensor using a heating resistor and a method of manufacturing thethermal sensor.

BACKGROUND OF THE INVENTION

At present, as fluid flow sensors that are installed in electroniccontrol fuel injection apparatuses of internal combustion engines ofvehicles, etc. and are used for air flow meters for measuring intake airquantity, the thermal type sensor has become mainstream because of itscapability of directly detecting mass air quantity.

Among these sensors, especially a thermal air flow sensor manufacturedby a semiconductor micromachining technology has attracted attentionsbecause it can reduce a cost and is drivable with a low electric power.There are the following documents as conventional technologies of airflow sensors like this. For example, Japanese Unexamined PatentApplication Publication No. S60 (1985)-142268 discloses an air flowsensor in which the heating resistor and a temperature measuringresistor (sensor) for measuring air flow rate are placed on a cavityformed by anisotropically etching a part of a Si substrate. Here, inJapanese Unexamined Patent Application Publication No. S60(1985)-142268,circuits of heater heating control, compensation of the flow rateoutput, and the like are produced on a different substrate. Therefore,the air flow rate detecting substrate and the circuit substrate need tobe wire-connected by wire bonding, which gives problems of an increasedcost caused by an increase in the number of parts, an increase in thenumber of processes by additional inspection after each assembly,lowering in a yield by assembly failure, etc.

There is Japanese Unexamined Patent Application Publication No.2008-157742 as a technology for addressing these problems. This documentdiscloses a thermal air flow meter in which a circuit part including MOStransistors and diode elements and a flow rate detection part having adiaphragm made by removing the Si substrate are formed on the samesubstrate. Therefore, a hard wiring process, such as the above-mentionedwire bonding, becomes unnecessary, and components can be reduced incount.

SUMMARY OF THE INVENTION

However, in Japanese Unexamined Patent Application Publication No.2008-157742, since the insulating film configurations of the circuitpart and a flow rate detection part are set identical and the protectivefilm by a thick inorganic insulating film that is the uppermost layer ofthe circuit part is also formed in the air flow rate detection part,there is a problem that a heat quantity of a heater is deprived by theprotective film and its sensitivity falls.

Moreover, in Japanese Unexamined Patent Application Publication No.2008-157742, there is a problem that since the protective film that is acircuit part uppermost layer is located even over the upper layer of theflow rate detection part, when a heater of the flow rate detection partis heated, a residual stress of the protective film varies, andresistance values of the heater and a sensor vary from their initialvalues, which deteriorates measurement accuracy. Since the protectivefilm is on the wiring layer for connecting a MOS transistor, the heater,and the sensor, the inorganic insulating film formed at a lowtemperature of 400° C. or less is usually used. Since the inorganicinsulating film formed at a low temperature like this has a large stressvariation by heat, the above-mentioned problem that the residual stressvaries becomes notable specially.

Based on the above points, an object of the present invention is to formthe detection part having a heating resistor and a control circuit forcontrolling the heating resistor on the same substrate and to provide ahigh-sensitivity and high-precision thermal sensor.

According to one aspect of the present invention, there is provided athermal sensor that has: a semiconductor substrate; a first layered filmthat is provided above the semiconductor substrate and includes multipleinsulating films; the detection part that is provided on the firstlayered film layer and has the heating resistor; the circuit part thatis provided on the semiconductor substrate and controls the heatingresistor; a second layered film that is provided on the heating resistorand above the control circuit, and includes multiple insulating films;an intermediate layer provided on the second layered film; and a thirdlayered film that is provided on the intermediate layer and above thecontrol circuit, and includes multiple insulating films; wherein theintermediate layer is made up of any one of aluminum nitride, aluminumoxide, silicon carbide, titanium nitride, tungsten nitride, and titaniumtungsten.

According to another aspect of the present invention, there is provideda thermal sensor that has: the semiconductor substrate; the firstlayered film that is provided above the semiconductor substrate andincludes multiple insulating films; the detection part that is providedon the first layered film and has the heating resistor; the circuit partthat is provided on the semiconductor substrate and controls the heatingresistor; the second layered film that is provided on the heatingresistor and above the control circuit, and includes multiple insulatingfilms; the intermediate layer provided on the second layered film; andthe third layered film that is provided in a region on the intermediatelayer from which a portion above the detection part is excluded.

According to still another aspect of the present invention, there isprovided a method of manufacturing the thermal sensor that is equippedwith the detection part having the heating resistor and the circuit parthaving the control circuit for controlling the heating resistor,including: (a) forming the first layered film including multipleinsulating films above the semiconductor substrate; (b) forming theheating resistor on the first layered film; (c) forming the controlcircuit on the semiconductor substrate; (d) forming the second layeredfilm including multiple insulating films on the heating resistor andabove the control circuit; (e) forming the intermediate layer on thesecond layered film; (f) forming the third layered film includingmultiple insulating films on the intermediate layer: and (g) etching aportion in the third layered film located above the detection part usingthe intermediate layer as an etch stop layer.

According to the aspects of the present invention, there can be provideda highly sensitive and highly reliable thermal sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a main part plan view showing one example of a thermal fluidflow sensor according to a first embodiment of the present invention;

FIG. 2 is a main part sectional view of the thermal fluid flow sensoraccording to the first embodiment of the present invention;

FIG. 3 is a main part sectional view showing a semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 4 is a main part sectional view showing the semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 5 is a main part sectional view showing the semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 6 is a main part sectional view showing the semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 7 is a main part sectional view showing the semiconductor substratemanufacturing process, of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 8 is a main part sectional view showing the semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 9 is a main part sectional view showing the semiconductor substratemanufacturing process of the thermal fluid flow sensor according to thefirst embodiment of the present invention;

FIG. 10 is a main part sectional view showing the semiconductorsubstrate manufacturing process of the thermal fluid flow sensoraccording to the first embodiment of the present invention;

FIG. 11 is a main part sectional view showing the semiconductorsubstrate manufacturing process of the thermal fluid flow sensoraccording to the first embodiment of the present invention;

FIG. 12 is a main part sectional view showing the semiconductorsubstrate manufacturing process of the thermal fluid flow sensoraccording to the first embodiment of the present invention;

FIG. 13 is a main part sectional view showing the semiconductorsubstrate manufacturing process of the thermal fluid flow sensoraccording to the first embodiment of the present invention;

FIG. 14 is an outline layout drawing of a thermal air flow meter onwhich the thermal fluid flow sensor according to the first embodiment ofthe present invention attached to an intake passage of an internalcombustion engine, such as of a vehicle, is installed;

FIG. 15 is a semiconductor substrate main part sectional view showingone example of a thermal fluid flow sensor according to a secondembodiment of the present invention; FIG. 16 is a semiconductorsubstrate main part sectional view showing one example of a thermalfluid flow sensor according to a third embodiment of the presentinvention;

FIG. 17 is a semiconductor substrate main part sectional view showingone example of a thermal fluid flow sensor according to a fourthembodiment of the present invention;

FIG. 18 is a main part plan view showing one example of a thermal fluidflow sensor according to a fifth embodiment of the present invention;and

FIG. 19 is a main part sectional view of the thermal fluid flow sensoraccording to the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of the present invention will be described,referring to drawings. Note that in the following embodiments, althoughexplanations are given using thermal fluid flow sensors especially asexamples of a thermal sensor, the invention of the application can besimilarly applied to other sensors each using a heating resistor in adetection part, for example, a humidity sensor etc.

Moreover, in the following embodiments, a term “above” indicates adirection into which the detection part and a circuit part are formed (adirection into which insulating films etc. are layered) of directionsperpendicular to the surface of a semiconductor substrate.

First Embodiment

FIG. 1 shows one example of a main part plan view of a thermal fluidflow sensor according to a first embodiment; FIG. 2 shows a main partsectional view taken along line A-A of FIG. 1.

As shown in FIG. 1 and FIG. 2, on a semiconductor substrate 2 mounted ona lead frame 1, the following are formed: an air flow rate measurementpart 3 for detecting a flow rate of a fluid; a circuit part 4 forcontrolling heater heating on which MOS transistors, diodes, memory,etc. are formed; and electrodes 5 for input/output to/from the outside.A diaphragm structure 8 whose backside Si was removed is provided in theair flow rate measurement part 3. Moreover, the electrodes 5 andexternal terminals 7 of the lead frame are connected together throughwire bonding 6, respectively. The circuit part 4 is supplied powersource from the outside through these electrodes 5 and the externalterminals 7 and outputs an air flow rate to the outside. Incidentally, apart in the semiconductor substrate 2 other than the air flow ratemeasurement part 3 is covered with a resin mold 9.

Next, one example of the method of manufacturing the thermal sensor inthe first embodiment will be explained in a process order using FIG. 3to FIG. 13. FIGS. 3 to 13 are main part sectional views showing indetail the semiconductor substrate 2 in FIG. 2.

First, as shown in FIG. 3, a semiconductor substrate 10 made up ofsingle crystal Si is prepared. Following this, a silicon oxide film 11is formed on the semiconductor substrate 10 with a furnace body, asilicon nitride film 12 is formed using a CVD method, subsequently,patterning is performed using a photolithography method, and a thicksilicon oxide film 13 for element isolation is formed by a process ofthermally oxidizing a portion where the insulating film 11 and theinsulating film 12 were removed at a high temperature. The silicon oxidefilm 13 at this time has a thickness of about 300 to 600 nm. Next, theinsulating film 11 and the insulating film 12 are removed, a siliconoxide film 14 are again formed on a Si substrate surface to a thicknessof 150 to 200 nm in the furnace body, subsequently, a silicon nitridefilm 15 using a CVD method is formed to a thickness of about 100 to 200nm, and patterning is performed using a photolithography method so thatthe silicon oxide film 14 and the silicon nitride film 15 may remainonly on the air flow rate detection part.

Next, as shown in FIG. 4, phosphorus, boron, or arsenic is implantedinto a region of the substrate corresponding to the circuit part on thesubstrate by implantation after washing to form a diffusion layer 16.Incidentally, in a region where implantation is not required, thesilicon oxide film 14 and the silicon nitride film 15 are made to remainat the time of the patterning.

Next, as shown in FIG. 5, after making the diffusion layer 16 clean bywashing, a gate oxide film 17 is formed by a thermal oxidation processwith the furnace body, then a poly-silicon film is formed, andpatterning by a photolithography method is performed to form a gateelectrode 18. Incidentally, although the film thickness of the gateoxide 17 depends on the circuit characteristic, it is about 5 to 30 nmand the film thickness of the gate electrode is about 100 to 150 nm.After this, ion implantation by an ion implanter is performed to form adiffusion layer 19 that is used as a source and a drain. Moreover, whenthe characteristic of a MOS transistor is altered according to a circuitcharacteristic, the kind of ion to be implanted, an ion implantationdose, the thickness of the gate oxide film, and a gate electrodematerial are changed, a transistor that matches each characteristic isformed by repeating the method of manufacturing the MOS transistor.

Next, as shown in FIG. 6, an insulating film 20 is formed thick and theinsulating film 20 is planarized using a CMP method or etching backmethod. Incidentally, the insulating film 20 is a silicon oxide filmcontaining boron or phosphorus or a silicon oxide film formed using aplasma CVD method. After the planarization, an insulating film 21 and aninsulating film 22 are formed sequentially to form a layered film.Incidentally, the insulating film 21 is a silicon nitride film formedby, for example, using a CVD method and its thickness is about 100 to200 nm; the insulating film 22 is a silicon oxide film formed by, forexample, using a CVD method, and its film thickness is about 100 to 200nm. Incidentally, the insulating films 14, 19, and 21 are films thathave a compressive stress whose residual stress is 50 MPa to 250 MPa;the insulating films 15, 20 are films that have a tensile stress of 700MPa to 1200 MPa. Incidentally, after each process, especially afterformation of the silicon oxide film using a CVD method and the siliconnitride film using a plasma CVD method, it is advisable to perform aheat treatment at 850° C. or more, preferably at 1000° C., on them in afurnace body or in a lamp heating apparatus under a nitrogen atmospherein order to make the film dense. Moreover, although the insulating film21 and the insulating film 22 were formed after the CMP in what wasdescribed above, the process of forming the insulating film 21 and theinsulating film 22 may be deleted by stress adjustment of the whole.

Next, as shown in FIG. 7, a metal plug 23 is formed as follows: acontact hole for making connection with a source and a drain 19 of thecircuit part and a contact hole for making contact with the gateelectrode 18, which is not shown in FIG. 7, are formed; a titaniumnitride (TiN) film by a sputtering method or CVD method is formed;following this, a tungsten (W) film by a CVD method is embedded into thecontact holes; and the W film in a region other than the holes isremoved by the etching back method or CMP method. After this, as aheater of the fluid flow rate detection part and as a metal film of thesensor, a Mo (molybdenum) film is formed by a sputtering method to 100to 250 nm. In doing this, in order to improve adhesiveness and improvecrystallinity, the ground layer insulating film 22 is etched by asputter etching method using Ar (argon) gas by about 5 to 22 nm beforethe deposition of Mo, and the Mo film is deposited at a substratetemperature of 200° C. to 500° C. Moreover, in order to further improvethe crystallinity of the Mo film, it is advisable to perform a heattreatment at 800° C. or more, preferably at 1000° C., on the Mo film inthe furnace body or the lamp heating apparatus under a nitrogenatmosphere after the formation of the Mo film. Next, using aphotolithography method, a metal film 24 is patterned to form the heaterand the sensor of the flow rate detection part. Incidentally, the samemetal film 24 as that of the heater and the sensor is placed on themetal plug 23, so that the metal plug 23 is not etched at the time ofprocessing the heater film 24. Incidentally, although a lamination ofTiN and W was mentioned as materials of the metal plug 23, it may bemade of only W or Poly-Si. Moreover, as means for improving thecrystallinity of the metal film 24 of the heater and the sensor, analuminum nitride film (AlN) may be formed as a ground layer. It ispreferable that the film thickness of the aluminum nitride film shouldbe about 20 to 100 nm.

Next, as shown in FIG. 8, an insulating film 25, an insulating film 26,and an insulating film 27 are sequentially formed to form a layered filmof multiple insulating films. The insulating film 25 is a silicon oxidefilm formed by, for example, a CVD method or a low-temperature CVDmethod that uses TEOS (tetraethoxysilane) as a raw material with plasma,and its film thickness is about 300 to 500 nm. The insulating film 26 isa silicon nitride film formed by, for example, a CVD method orlow-temperature CVD method, and its film thickness is about 150 to 200nm. The insulating film 27 is a silicon oxide film formed by, forexample, a CVD method or a low-temperature CVD method that uses TEOS asa raw material with plasma, and its film thickness is about 100 to 500nm. Incidentally, the insulating films 25, 27 are films that have acompressive stress whose residual stress is 50 MPa to 250 MPa; theinsulating film 26 is a film that has a tensile stress of 700 MPa to1400 MPa. By performing the heat treatment at 850° C. or more,preferably 1000° C., after the film formation by deposition, theinsulating film 26 is adjusted so as to have a desired tensile stress.Similarly, by performing the heat treatment at 850° C. or more,preferably 1000° C., after the film formation by deposition, the oxidesilicon films of the insulating films 25, 27 are also adjusted so as tohave a desired compressive stress. Although the above heat treatment maybe performed collectively after the insulating films 25 to 27 areformed, preferably, it is advisable to perform the heat treatmentsequentially as follows: film formation and heat treatment of theinsulating film 25 is performed; subsequently, the same processing andtreatment are performed on the insulating film 26; and after that, thesame processing and treatment are performed on the insulating film 27.This is because a moisture resistance of each of the insulating films 25to 27 will be improved by these heat treatments. Moreover, by performingthe heat treatment, each of the insulating films 25 to 27 becomes aninsulating film whose residual stress is resistant to variation evenwhen the heater heating is performed at the time of a flow ratemeasurement. As a result, it is possible to suppress aging variation ofthe resistance of the insulating film by the heater heating in alongtime.

Next, as shown in FIG. 9, a connection hole is formed by a dry etchingmethod, a wet etching method, or the like. Subsequently, a layered filmof an Al alloy film of a thickness of, for example, about 400 to 800 nmis formed as a first wiring metal film for connecting the circuit partand the fluid flow rate detection part. Incidentally, in order to makegood contact with the metal film 24 exposed in the connection hole, asurface of the Mo film may be sputter etched with Ar (argon) gas beforethe formation. Furthermore, in order to make the contact positive,layered film structures as follows may be formed: a two-layer film of abarrier metal film, such as a TiN film, and an Al alloy film, thebarrier film being formed before deposition of the Al alloy; and athree-layer film realized by further forming a TiN film on the Al filmof the two-layer film. In doing this, the thickness of the barrier metalfilm is desirable to be 200 nm or less. Moreover, although the TiN filmis mentioned as the barrier metal film, a TiW (titanium tungsten) film,a Ti (titanium) film, and a layered film of these may be applicable.Next, the first wiring metal film is patterned using a photolithographymethod, and a first wiring layer 28 is formed by a dry etching method orwet etching method.

Here, as shown in FIG. 9, when forming the metal film 24 as the heatingresistor, a metal film 24 that is provided on the same layer as theheating resistor can be further formed between the wiring layer 28 andcontrol circuits (16 to 19). This is because when forming the wiringlayer 28, a hole for taking contact with it must be formed by etching tothe insulating films 25 to 27, but formation of the metal film 24 on theupper part of the metal plug 23 makes it possible to suppress damage tothe metal plug 23 caused by the etching.

Next, as shown in FIG. 10, an insulating film 29 and an insulating film30 are formed. Note that the insulating film 29 needs to be a materialwith a larger selection ratio at the time of etching than inorganicinsulating films that will be formed after this. Specifically, amaterial that has a high selection ratio of more than 30, preferablymore than 50, with respect to the inorganic insulating film is,advisable. Specifically, applicable materials are an aluminum nitride(AlN) film, an aluminum oxide (AlO) film, a silicon carbide (SiC) film,etc. Here, it is desirable that the film thickness of the insulatingfilm 29 should be 200 nm or less. This is for reducing an influence ofthe residual stress by the insulating film 29. Especially preferably,the film thickness is about 20 to 100 nm. This is because ease ofremoval when removing the insulating film 29 later should be considered.Here, the above-mentioned selection ratio of the insulating film 29means a selection ratio when etching (for example, in the case of dryetching, etching using a fluorine-containing gas, and in the case of wetetching, an aqueous solution of hydrofluoric acid (ex., a dilutedsolution of hydrofluoric acid)) for removing the inorganic insulatingfilm is performed. The insulating film 30 is an oxide silicon filmformed by, for example, a CVD method or a low-temperature CVD methodthat uses TEOS as a raw material with plasma, and its film thickness isabout 100 to 500 nm. After this, a connection hole of the first wiring,layer or the metal film 24 and a connection hole of the second wiringlayer 28 that will be formed later is formed by a dry etching method, awet etching method, or the like. In doing this, after forming theconnection hole in the insulating film 30, for etching at the time offorming the connection hole in the insulating film 29, if in the case ofthe dry etching, a gaseous species is changed from a fluorine-containinggas to a chlorine-containing gas in order to remove the insulating film29. On the other hand, if the etching is wet etching, an etchant ischanged from a hydrofluoric acid diluted solution to an alkaline systemliquid (KOH or TMAH). Subsequently, a layered film of an Al alloy filmof a thickness of, for example, about 400 to 1000 nm is formed as asecond wiring metal film for connecting the circuit part and the fluidflow rate detection part. Incidentally, in order to make good contactwith the first wiring layer 28 that is a ground layer, a surface of thefirst wiring layer 28 may be sputter etched with Ar (argon) gas beforethe formation. Furthermore, in order to make the contact positive, thefollowing layered film structures may be formed: a two-layer film of abarrier metal film, such as a TiN film, and an Al alloy film, thebarrier film being formed before the deposition of the Al alloy; athree-layer film made by further forming a TiN film on the Al film ofthe two-layer film; and the like. In doing this, it is desirable thatthe thickness of the barrier metal film should be 200 nm or less.Moreover, although the TiN film was mentioned as the barrier metal film,a TiW (titanium tungsten) film, a Ti (titanium) film, and a layered filmof these may be applicable. Next, the second wiring metal film ispatterned using a photolithography method, and a second wiring layer 31is formed by a dry etching method or wet etching method.

Next, as shown in FIG. 11, an insulating film 32 and an insulating film33 are formed to form a layered film. The insulating film 32 is asilicon oxide film formed by, for example, a CVD method or alow-temperature CVD method that uses TEOS as a raw material with plasma,and its film thickness is about 300 to 800 nm. The insulating film 33 isa silicon nitride film formed by, for example, a CVD method or alow-temperature CVD that uses plasma. In order to suppress damage to thetransistors and the wiring caused by filler at the time of resin moldformation and to prevent corrosion of the wiring caused by moisturepenetration from the outside, it is formed thick to have a filmthickness of about 800 to 1200 nm.

Next, as shown in FIG. 12, patterning is performed using aphotolithography method, and an insulating film 32 and an insulatingfilm 33 on an electrode 34 for connection with the outside (indicatingportions in the second wiring layer 31 where the upper layer insulatingfilms 32, 33 were removed to form pads; similarly hereafter) are removedby dry etching. At this time, the insulating film 33, the insulatingfilm 32, and the insulating film 30 above the flow rate detection partare removed by dry etching to form an opening 35. Incidentally, since inthe portion for detecting the flow rate, the insulating film 29 acts asan etch stop layer of the dry etching, the insulating film that controlsthe residual stress of underlying layers beneath this layer is notaffected by influences of over-etching of the dry etching and anin-plane distribution; therefore, it becomes possible to form theinsulating film being controlled within a range of a designed filmthickness and within a range of the residual stress.

Next, as shown in FIG. 13, a polyimide film, for example, is formed asan organic protective film 36, and is made into a shape such that atleast parts of the polyimide film over both the electrode 34 forconnection with the outside and an air flow rate detection part 37 areremoved using a photolithography method. Next, a resist pattern isformed on the backside of the semiconductor substrate 10 by aphotolithography method, the insulating films 14, 15 formed on thebackside are removed by a dry etching or wet etching method, andsubsequently, the backside of the Si substrate is wet etched with anaqueous solution whose main ingredient is KOH (potassium hydrate), TMAH,or the like using the remaining insulating films 14, 15 as masks to forma diaphragm 38. Incidentally, the diaphragm 38 is designed to be largerthan the flow rate detection part 37 of the protective film 36.Preferably, each side of the diaphragm 38 is formed to be larger thaneach side of the flow rate detection part 37 of the protective film 36by about 50 gm or more. This is because a portion in the protective film36 inside the outer circumference of the diaphragm 38 has an effect ofprotecting the diaphragm from dust mixed with air from the outside. Itis desirable that the total film thickness of the inorganic insulatingfilms that constitute this diaphragm 38 should be 1.5 μm to 2.5 μm. Thisis because if it is thinner than these values, strength of the diaphragm38 will decrease, and a probability that it will be destroyed bycollision of dust contained in air intake of a vehicle.

Incidentally, although the thermal fluid flow sensor whose metal film 24of the heater and the sensor was made up of Mo was explained, thefollowing metal films will do: a metal made up of any one of elements ofα-Ta (alpha tantalum), Ti (titanium), W (tungsten), Co (cobalt), Ni(nickel), Fe (iron), Nb (niobium), Hf (hafnium), Cr (chromium), and Zr(zirconium) as a main element, for example; and a films made up of anyone of metal nitride compounds, such as TaN (nitride tantalum), MoN(nitride molybdenum), and WN (tungsten nitride), metal silicidecompounds, such as MoSi (molybdenum silicide), CoSi (cobalt silicide)and NiSi (nickel silicide), and polycrystalline silicon with phosphorusor boron doped as an impurity, respectively.

When based on the foregoing, features of the method of manufacturing thethermal sensor according to this embodiment are as follows. That is, itis a method of manufacturing the thermal sensor that is equipped withthe detection part (3) having a heating resistor, and the circuit part(4) having the control circuit for controlling the heating resistor,comprising the steps of: (a) forming a first layered film (20 to 22)including multiple insulating films above the semiconductor substrate;(b) forming the heating resistor (24) on the first layered film; (c)forming the control circuits (16 to 19) on the semiconductor substrate;(d) forming a second layered film (25 to 27) including multipleinsulating films on the heating resistor and above the control circuit;(e) forming an intermediate layer (29) on the second layered film; (f)forming a third layered film (30, 32, 33) including multiple insulatingfilms on the intermediate layer; and (g) etching a portion in the thirdlayered film located above the detection part using the intermediatelayer as an etch stop layer (FIG. 12).

Moreover, when paying attention to a structural, aspect of the thermalsensor, features of the invention according to this embodiment will beas follows (FIG. 13). That is, provided is a thermal sensor that has:the semiconductor substrate; the first layered film that is providedabove the semiconductor substrate and includes multiple insulatingfilms; the detection part that is provided on the first layered film andhas the heating resistor; the circuit part that is provided on thesemiconductor substrate and has the control circuit for controlling theheating resistor; the second layered film that is provided on theheating resistor and above the control circuit, and includes multipleinsulating films; the intermediate layer provided on the second layeredfilm; and the third layered film that are provided in a region on theintermediate layer from which a portion above the detection part isexcluded, and includes multiple insulating films.

This thermal sensor and the method of manufacturing it give thefollowing effects. That is, in the circuit part, protection of thewiring and improvement of moisture resistance by the layered film 30,32, and 33 are realized. Simultaneously, in the detection part, sincethe layered film has been removed, it has a desired residual stress thatwas designed by the layered film 20 to 22 and the layered film 25 to 27.In addition, since the heat quantity of the heater is not deprivedthrough the layered film 30, 32, and 33, it realizes improvement ofaccuracy of the heater.

Next, in the above-mentioned step (e), it is characterized in thatespecially the intermediate layer is specified to be any one of aluminumnitride, aluminum oxide, and silicon carbide.

Moreover, when paying attention to the structure of the thermal sensor,features of this invention will be as follows. That is, provided is athermal sensor that has: the semiconductor substrate; the first layeredfilm that is provided above the semiconductor substrate and includesmultiple insulating films; the detection part that is provided on thefirst layered film and has the heating resistor; the circuit part thatis provided on the semiconductor substrate and has the control circuitfor controlling the heating resistor; the second layered film that isprovided on the heating resistor and above the control circuit, andincludes multiple insulating films; the intermediate layer provided onthe second layered film; and the third layered film that is provided onthe intermediate layer and above the control circuit, and includesmultiple insulating films, wherein the intermediate layer is made up ofany one of aluminum nitride, aluminum oxide, and silicon carbide.

This is because these materials have larger selection ratios in thefluorine-containing material dry etching or in wet etching withhydrofluoric acid aqueous solution than materials constituting theinsulating films 30, 32, and 33 (for example, silicon oxide and siliconnitride) that make up the layered film does, and functions effectivelyas the etch stop layer to the layered film.

Moreover, the opening 35 has a relationship of being larger than thediaphragm 38. That is, portions of the layered film 30, 32, and 33 areremoved so that it may have a larger area than the diaphragm 38 to formthe opening 35. This is to prevent the residual stress of a detectionpart 3 from varying by making the layered film 30, 32, and 33 remain onthe upper part of the diaphragm 38.

FIG. 14 is an outline layout drawing of a thermal air flow meter towhich the thermal fluid flow sensor attached to an intake passage of aninternal combustion engine of a vehicle etc. is installed according tothe first embodiment of the present invention. A thermal air flow meter44 consists of a measurement element 1 that is the thermal fluid flowsensor, a support member 42, and a link part 43 for electricallyconnecting the outside and the measurement element 1, and themeasurement element 1 is placed in a sub passage 41 located in theinterior of the air passage 40. Intake air 45 flows in a direction ofair flow shown by an arrow of FIG. 14 or in a direction opposite to thisdepending on a condition of the internal combustion engine.

Second Embodiment

The thermal fluid flow sensor according to a second embodiment isdifferent from that of the first embodiment in that it has a structuresuch that the insulating film 29 acting as the etch stop layer isremoved from the uppermost layer of the flow rate detection part 37 ascompared with that of the first embodiment.

FIG. 15 is one example of a thermal fluid flow sensor according to thesecond embodiment, showing a main part sectional view of thesemiconductor substrate 2. Since the thermal fluid flow sensor accordingto the second embodiment has many common components as those of thefirst embodiment, detailed explanations are omitted for the commoncomponents and components that are different will be explainedselectively. Incidentally, the same reference numerals are used for thesame components as the components shown in the first embodiment,respectively.

Although in the first embodiment, a structure such that the insulatingfilm 29 acting as the etch stop layer is left on the uppermost layer ofthe flow rate detection part 37 is used; it is characterized in that ifthe film thickness of the insulating film 29 is thick, which destroys astress balance of the whole flow rate detection part 37, the insulatingfilm 29 will be removed using the organic protective film 36 as a mask,as shown in the second embodiment. Adoption of this structure makes itpossible to control the residual stress of the flow rate detection part37, producing an effect of improved reliability. Here, a process ofremoving the insulating film 29 is performed by etching that uses achlorine-containing gas in the case of dry etching or an alkaline systemsolution (KOH or TMAH) in the case of wet etching. Moreover, also in theprocess of forming the connection hole of the first wiring layer or themetal film 24 and the first wiring layer 28, which was described in thefirst embodiment, the insulating film 29 needs to be removed. The numberof steps can be curtailed also by removing the insulating film 29 abovethe flow rate detection part 37 in that process.

Incidentally, although the organic protective film 36 was used as themask in the second embodiment, a method of, before forming the organicprotective film 36, i.e., after forming the opening 35 by removing theinsulating film 33, the insulating film 32, and the insulating film 30by dry etching, removing the insulating film 29 acting as the etch stoplayer consecutively also give the same effect as that of the secondembodiment.

Third Embodiment

A third embodiment has a structure that a metal film is adopted as theetch stop layer.

FIG. 16 shows one example of a thermal fluid flow sensor according tothe third embodiment, showing a main part sectional view of thesemiconductor substrate 2. Since the thermal fluid flow sensor accordingto the third embodiment has many common components as those of the firstembodiment, detailed explanations are omitted for the common componentsand components that are different will be explained selectively.Incidentally, the same reference numerals are used for the samecomponents as the components shown in the first embodiment,respectively.

Although the insulating film 29 acting as the etch stop layer was usedin the first embodiment, the metal film 39 acting as the etch stop layeris formed instead of the above-mentioned insulating film in the thirdembodiment. FIG. 16 shows especially a structure such that the metalfilm 39 acting the etch stop layer is removed from the uppermost layerof the flow rate detection part 37 similarly with the second embodiment.However, a structure such that the metal film being the uppermost layerof the flow rate detection part 37 is left similarly with the firstembodiment is also possible.

The metal film 39 acting the stop layer is processed as follows: the Alfilm is processed using the barrier film used for the first wiring layer28, such as of titanium nitride (TiN), tungsten nitride (WN), titaniumtungsten (TiW), etc.; the Al film is patterned using a photolithographymethod again so as to cover a wider area than the flow rate detectionpart 37 and the diaphragm 38; and a portion that serves as the metalfilm 39 is left in the Al film. Note that in this process, the metalfilm 39 is not left on respective upper layers of the wiring layer 28,as a point different from the first and second embodiments. This isbecause if the metal film 39 is allowed to remain at these positions,mutual conduction will be established between them and the first wiringlayer 28.

After this, the process proceeds similarly with the first embodiment:the opening 35 is processed by dry-etching the insulating film 33, theinsulating film 32, and the insulating film 30; and subsequently theorganic protective film 36 is formed and patterned. Thereby the thirdembodiment attains the same effect as that of the first embodiment.Furthermore, by removing the metal film 39 acting the etch stop layerafter that, the same effect as that of the second embodiment can beattained.

Summarizing the foregoing, the method of manufacturing the thermalsensor according to this embodiment is characterized in that theintermediate layer is especially specified to be any one of titaniumnitride, tungsten nitride, and titanium tungsten in step (e) accordingto the first embodiment described above.

Moreover, when paying attention to the structural aspect of the thermalsensor, features of this invention will be as follows. That is, providedis a thermal sensor that has: the semiconductor substrate; the firstlayered film that is provided above the semiconductor substrate andincludes multiple insulating films; the detection part that is providedon the first layered film and has the heating resistor; the circuit partthat is provided on the semiconductor substrate and has the controlcircuit for controlling the heating resistor; the second layered filmthat is provided on the heating resistor and above the control circuit,and includes multiple insulating films; the intermediate layer providedon the second layered film; and the third layered film that is providedon the intermediate layer and above the control circuit, and includesmultiple insulating films, wherein the intermediate layer is made up ofany one of titanium nitride, tungsten nitride, and titanium tungsten.

This is because these materials function as the etch stop layer to thelayered film 30, 32 effectively similarly with the above-mentionedinsulating films such as of aluminum nitride.

Incidentally, although the organic protective film 36 was used as themask in what was described above, the same effect as that of the secondembodiment can be attained also by, before the organic protective film36 is formed, namely, after the opening 35 is processed by dry etchingthe insulating film 33, the insulating film 32, and the insulating film30, removing the metal film 39 acting as the etch stop layersequentially,

Fourth Embodiment

This fourth embodiment has a configuration in which the metal film 24that is on the same layer as the metal film forming the heater and thesensor is used as wiring of the circuit part.

FIG. 17 shows one example of a thermal fluid flow sensor according to afourth embodiment, showing a main part sectional view of thesemiconductor substrate 2. Since the thermal fluid flow sensor accordingto the fourth embodiment has many common components as those of thefirst embodiment, detailed explanations are omitted for the commoncomponents and components that are different will be explainedselectively. Incidentally, the same reference numerals are used for thesame components as the components shown in the first embodiment,respectively.

In the first embodiment, the first wiring layer 28 is used forconnection of the flow rate detection part 3 and the circuit part 4 andconnection inside the circuit part, and the second wiring layer 31 isused for connection of wiring inside the circuit and the outside. Thisfourth embodiment has a configuration in which the metal film 24 usedfor the heater and the sensor is used as a wiring layer for realizingwiring inside the circuit to omit the second wiring layer 31 shown inFIG. 13, and the electrode 34 for connection with the outside is givenas the first wiring layer 28. That electrode 34 is formed simultaneouslywith the above-mentioned opening 35 (step (g)).

That is, the method of manufacturing the thermal sensor according tothis embodiment is characterized by further comprising a step of forminga wiring layer (28) for connecting the heating resistor and the controlcircuit before step (f) of the first embodiment described above, andfurther etching a portion in the third layered film located above thewiring layer in step (g).

Moreover, when paying attention to the structural aspect of the thermalsensor, features of this invention will be as follows. That is, providedis a thermal sensor that further has a wiring layer for connecting theheating resistor and the control circuit, and is characterized in thatan electrode for connecting the control circuit and the outside of thethermal sensor is formed on the wiring layer.

By taking this configuration, it becomes possible to attain the sameeffect as that of the first embodiment and to form the electrode 34simultaneously with the formation of the opening 35; therefore,manufacturing steps can be curtailed and cost reduction can be attained.

Fifth Embodiment

FIG. 18 is one example of a thermal fluid flow sensor according to thisfifth embodiment, and FIG. 19 is a main part sectional view taken alongline B-B of FIG. 18. Since the thermal fluid flow sensor according tothe fifth embodiment has many components in common with those accordingto the first embodiment, detailed explanations of the common componentsare omitted and different components will be explained selectively.Incidentally, the same reference numerals are used for the samecomponents as the components shown in the first embodiment,respectively.

Although in this fifth embodiment, the semiconductor substrate 2 mountedon the lead frame 1 and connection between the electrodes 5 forinput/output to/from the outside and the external terminals 7 of thelead frame by wire bonding 6 are the same as those of the firstembodiment, but it has a notable feature in how the resin mold 9 coversthe substrate 2. This embodiment has a structure such that at least theentire lead frame 1 is covered with the resin mold 9, a region includingat least the diaphragm 8 of the flow rate detection part 3 of thesemiconductor substrate 2 is exposed, and a groove 47 is formed along adirection in which air flows. By placing a lid (not illustrated) made ofanother material on this groove 47, a flow passage of air can be formedsimply and with excellent accuracy. Moreover, since this embodimentenables adjustment of the air flow rate that is important in measuringthe air flow rate to be performed simply by changing the thickness ofthe resin mold 9 or by changing a shape of the groove 47, a shape of thelid, etc., it is possible to simplify an assembly process and thereby toattain cost reduction.

Incidentally, at least, the organic protective film 36, the insulatingfilm 33, and the insulating film 32 are formed in the underlying layerin a structure of the semiconductor substrate 2 to which the resin moldcontacts, and these films protect the structure from a shock by fillerat the time of resin mold formation.

Moreover, although the example in which the flow rate detection part andthe circuit part are formed on the same substrate was mentioned in thisembodiment, the present invention is also applicable to a complex sensorin which other sensors, for example, a humidity sensor, a pressuresensor, etc. are formed.

What is claimed is:
 1. A method of manufacturing a thermal sensor thathas a detection part having a heating resistor and a circuit part havinga control circuit for controlling the heating resistor, the methodcomprising: (a) forming a first layered film including a plurality ofinsulating films above a semiconductor substrate; (b) forming theheating resistor on the first layered film; (c) forming the controlcircuit on the semiconductor substrate; (d) forming a second layeredfilm including a plurality of insulating films on the heating resistorand above the control circuit; (e) forming an intermediate layer on thesecond layered film; (f) forming a third layered film including aplurality of insulating films on the intermediate layer; and (g) etchinga portion in the third layered film located above the detection partusing the intermediate layer as an etch stop layer.
 2. The method ofmanufacturing the thermal sensor according to claim 1, wherein theintermediate layer is formed with any one of aluminum nitride, aluminumoxide, silicon carbide, titanium nitride, tungsten nitride, and titaniumtungsten in step (e).
 3. The method of manufacturing the thermal sensoraccording to claim 1, further comprising: etching a portion in theintermediate layer located above the detection part after the step (g).4. The method of manufacturing the thermal sensor according to claim 1,further comprising: forming a wiring layer for connecting the heatingresistor and the control circuit before the step (f), wherein a metallayer for connecting the wiring layer and the control circuit is furtherformed in the step (b).
 5. The method of manufacturing the thermalsensor according to claim 1, further comprising: forming a wiring layerfor connecting the heating resistor and the control circuit before thestep (f), wherein in the step (g), a portion in the third layered filmlocated above the wiring layer is further etched.